Owen Labrie breaks down as the mixed verdict is read on Friday. Link to video

A former New Hampshire prep school senior was found not guilty of raping a 15-year-old freshman days before graduation during an unofficial tradition at the elite school known as a “senior salute”.

The jury found Owen Labrie, 19, not guilty on three counts of aggravated rape, guilty of three counts of misdemeanor sex assault, guilty of a Class B felony for using a computer to lure the victim, guilty of endangering a child and not guilty of simple assault. Labrie faces three and a half to seven years in prison for the Class B felony of using Facebook and the school’s computer system to lure the victim, and up to one year in prison on each of the four misdemeanors.

Labrie wept as the mixed verdicts were read and struggled to stand. At one point, he folded his hands and looked skyward as if he was praying.

After the verdict was announced, the victim and her family released a statement through their attorney, thanking police and investigators and criticizing the school for fostering “a toxic culture that left our daughter and other students at risk to sexual violence.”

“While we stood together as a family through this process, it was our young daughter who took the stand to speak the truth and request justice. We admire her bravery in coming forward and speaking out in the face of great adversity. It is truly her courage that has made this measure of justice possible today,” they said.

Labrie, a top student and soccer player once headed for Harvard, claimed he took the girl to the roof of the St Paul’s school science center in Concord where he put on a condom during a consensual “romantic” encounter but decided against having sex.

The jury of nine men and three women heard testimony about the sexual culture at the insular boarding school, whose alumni include the secretary of state, John Kerry, and Pulitzer prize-winner Garry Trudeau. Annual tuition is more than $50,000.

Labrie of Turnbridge, Vermont, who attended the school on a scholarship, had been headed to Harvard on a full scholarship last year when he was indicted on rape charges. He had planned to study theology.

He maintained his innocence from his first contact with police and rejected prosecutors’ offers of a plea agreement that would have required him to plead guilty to sexual penetration, according to his attorney JW Carney Jr.

Prosecutors portrayed him as a sexual predator determined to win a contest of sexual conquests among his friends. The boys wanted to “slay” the most girls, a slang term they used in their electronic messages. In his testimony, Labrie’s roommate denied they had a competition and said he warned Labrie the girl was too young.

State prosecutor Joseph Cherniski told the jury Labrie “turned his lust for a 15-year-old girl into reality” in the dark attic of the science center and ignored her when she tried to pull him away from her genital area.

The dean of students from the school, Chad Green, testified he was aware of the senior salute tradition at St Paul and knew it could contain a sexual component.

“I came to understand the senior salute as one element of a larger vernacular the kids at St Paul’s used to describe a wide range of relations between students,” Green said.

Crude social media exchanges between Labrie and his friends about the accuser were presented as evidence. He admitted he and a friend drew up a list of girls they wanted to “slay” during their waning months of high school but denied the term meant sexual intercourse. The girl’s name was in capital letters.

In tearful testimony at the start of the trial last week, his accuser, now 16, said she willingly met Labrie and took off her sweatshirt and pants but never consented to sexual penetration and pulled his face away from her genital area.

A mutual friend of Labrie had convinced her she could trust him after she initially refused to see him.

The encounter in May 2014 left her in shock and unable to flee, she said. Minutes after the incident, she told friends, “I think I just had sex with Owen Labrie.”

DNA testing on the crotch of the accuser’s underwear did not find Labrie’s sperm but found his DNA, according to expert testimony.

After the verdict was read, the girl and her older sister hugged family members in the courthouse. In a statement, the family said they can never be part of the St Paul’s community again.

A statement is read on behalf of the family of the teenage girl, in which they say a ‘measure of justice has been served’

“We still feel betrayed by St Paul School as they allowed and fostered a toxic culture. They left our daughter and several other students at risk of sexual violence. We trusted the school to protect her and it failed us. We continue to feel anger and disappointment for the lack of character and integrity of the young men at St Paul School. They laughed and joked about slaying our daughter,” the family said.

The rector of the school commended “the remarkable moral courage and strength” shown by the girl.

Evidence at trial included numerous flirty emails between Labrie and the girl both before and after she accepted his invitation to meet him.

Labrie’s attorney Carney had accused the girl of falsely claiming rape after her sister confronted her about rumors that the young girl had sex with Labrie, whom the sister had briefly dated.

“In essence what the jury found is one teenager had consensual sex with another,” he said outside the courthouse.

Carney said the judge ran “an extraordinarily fair trial”. But he called the prosecution “overzealous” and said they misused the state law against enticement of a child via computer.

“Owen’s life will never be the same. This is like a tattoo or a brand he will wear the rest of his life. I’m sure he will spend the rest of his life showing people through his actions and his character [that] these convictions should not have occurred.”

Parents of his former St Paul classmates helped fund his legal defense.